Octalkoxy-Substituted Phosphorus(V) Triazatetrabenzcorroles via Ring Contraction of Phthalocyanine Precursors

A new class of oxo-bridged high-valent hexamanganese (Mn6) clusters containing a novel {Mn6O8}6+ core, [MnIV 4Mn III 2((mu)-O)4((mu)3-O)4(dmb)6(O2CR)2]4+ (where dmb = 4,4ʹ-dimethyl-2,2ʹ-bipyridine, and RCO2 = 2,6-di(p-tolyl)benzoate (Ar Tol CO2 -) (3) or 2,6-di(4-terf-butylphenyl)benzoate (Ar 4-tBuPh CO2 -) (4)), was synthesized using sterically hindered m-terphenyl-derived carboxylate ligands. These complexes can be synthesized by oxidizing the Mn II mononuclear complexes, [Mn(dmb)2(OH2)(O2CR)]+ (where RCO2 = Ar Tol CO2- (1) or Ar 4-tBuPh CO2- (2)) with (n-Bu4N)MnO4, by direct Mn(II) + Mn(VII) in situ comproportionation reactions, or by ligand substitution on the dinuclear manganese (III,IV) or (IV,IV) complexes, [(Mn2((mu)-O)2(dmb)4)]3+/4+ .The compound [Mn IV 4 Mn III 2 ((mu)-O)4((mu)3-O)4(dmb)6(Ar Tol CO2)2](OTf)4 [3(OTf)4] crystallizes in the monoclinic space group P2 1 /n, with the cell parameters a = 15.447(1) A, b = 15.077(2) A, c = 27.703(2) A, (beta) = 91.68(2)°, V= 6449.3(6) A^3 and Z= 2. The X-ray structure reveals that there are three different bridging modes for the oxo groups:(mu), "pyramidal" (mu)3, and "T-shaped" (mu)3. Solid-state variable temperature magnetic susceptibility studies suggest that the Mn centers are net antiferromagnetically coupled to yield a diamagnetic ST = 0 ground spin state with a large number of low-lying, thermally accessible states with ST > 0. 1H NMR spectra were recorded for both Mn6 clusters and selected resonances assigned. The electronic and redox properties of these complexes along with the effect of the presence of the bulky carboxylate ligands are also described here.